The present invention relates to a cathode for a magnetron used for microwave oscillation in a pulse radar device which is mounted on pleasure boats or on fishing boats, and especially to a technique for restraining consumption, omission or degradations of thermionic emission performance filled into the cathode.
A magnetron which is especially used for a radar is mostly operated in a pulse-like manner and an extremely large current density is generally expected for electron flow emitted from a cathode thereof. Due to this fact, a surface of this cathode receives inverse impulse from electrons or ions (impulse caused through ions or once emitted electrons returning back to the cathode) so that thermionic emitting materials such as oxides are consumed and decreased through sputtering, and the magnetron can no more perform accurate operations in case such phenomena repeatedly occur. In case no uniform current density can be obtained owing to lack in uniformity of particle sizes of the thermionic emitting materials, partial decreases in the thermionic emitting materials are caused to thereby shorten a life cycle of the magnetron.
In view of these facts, it has been proposed for a method of covering surfaces of base metals with a porous body or metallic mesh of good conductivity and filling thermionic emitting materials on corresponding portions thereof to thereby achieve uniformity of current density owing to good conductivity, and of controlling the degree of decrease of thermionic emitting materials by further adjusting hole rates of the porous body or fineness of reticulations of the mesh.
There are also known methods which are devised to make thermionic emitting materials uniformly decrease through further achieving uniformity of exposure of the thermionic emitting materials rather than adjusting holes or reticulations.
FIG. 12 is a view showing an arrangement of electrode portions of a conventional magnetron to which this kind of device is made. Numeral 1 denotes a cathode and 2 an anode. In the cathode 1, numeral 11X is a base metal of Ni or the like formed in a cylindrical shape with a plurality of concave grooves 131 being formed at a specified pitch in a peripheral direction of a surface thereof, 12 thermionic emitting materials of oxides of alkali earth metals or the like which are filled into these concave grooves 131, 13 a cathode supporting body (sleeve) which is fixedly attached to inside of the base metal 11X, and 14 a heater which is arranged in the interior of the cathode supporting body 13.
FIG. 13 is a view showing a base metal 11Y of another prior art wherein a plurality of concave grooves 132 are formed at a specified pitch in a direction parallel to an axial direction of a surface of the base metal 11Y and wherein thermionic emitting materials 12 are filled into these grooves.
FIG. 14 is a view showing a base metal 11Z of still another prior art wherein a plurality of concave pits 133 are formed on a surface of the base metal 11Z in a discrete manner through wet etching. Each concave pit 133 is so formed that an area of its bottom surface is larger than that of its aperture.
In these examples as illustrated in FIGS. 12 to 14, the thermionic emitting materials 12 filled into the concave grooves 131, 132 or the concave pits 133 of the base metals 11X, 11Y and 11Z are heated to nearly 800xc2x0 C. by the heater 14 whereby thermoelectrons are emitted from surfaces thereof which are exposed to the exterior. In case direct-current high voltage is impressed such that the cathode 1 is negative and the anode 2 is positive, and a magnetic field is impressed in vertical directions in the illustrated example of FIG. 12, electrons emitted from the thermionic emitting materials 12 are made to rapidly move (spin) in a peripheral direction in a space formed between the base metal 11X and the anode 2 to thereby generate microwaves.
However, in the case of cathodes of conventional arrangements utilizing base metals 11X, 11Y, 11Z as illustrated in the above FIGS. 12 to 14, while quantification of areas of the thermionic emitting materials 12 which are exposed to the exterior is performed, there are taken no measures for adjusting degrees of receiving inverse impulse from electrons or ions, and degrees of consumption and decrease are not improved. Although areas of bottom surfaces of the concave pits 133 are larger than their aperture areas by approximately several % (generally approximately 5%)in the arrangement of the base metal 11Z shown in FIG. 14, these shapes are formed through wet etching in a subordinate manner, and thus, the life cycle of the cathode is hardly different from those of the examples as illustrated in FIGS. 12 and 13.
Therefore, it is an object of the present invention to solve the above problems, and to provide a cathode for a magnetron which exhibits durability against inverse impulse from electrons or ions and which is of long life.
A first aspect of the present invention for solving the above problems relates to a cathode for a magnetron having concave/convex portions on a surface of a cylindrical base metal with thermionic emitting materials being fixedly attached to concave portions from among the concave/convex portions, wherein the convex portions of the concave/convex portions are arranged to be inclining.
In a second aspect of the present invention, the convex portions as recited in the first aspect are arranged to be inclining in a range of approximately 25 to 63 degrees in moving directions of electrons with respect to a normal line of the base metal.
In a third aspect of the present invention, areas of bottom surfaces of the concave portion of the concave/convex portions as recited in the first or second aspect are arranged larger than areas of apertures of the concave portion by at least 10%.
In a forth aspect of the present invention, the base metal as recited in the first or second aspect is formed of a material formed by cold drawing or a material formed by cold extrusion, and the concave portions of the concave/convex portions are composed of a plurality of concave grooves extending in a direction parallel to an axial direction of the base metal.
In a fifth aspect of the present invention, the concave portions of the concave/convex portions as recited in the first or second aspect are either formed of a plurality of concave grooves which are formed in a direction parallel to an axial direction of the base metal, a plurality of concave grooves which are formed in a direction intersecting the axial direction, a single concave groove which is formed in a threaded shape in a direction diagonal to the axial direction, or a plurality of concave pits which are discretely formed, wherein a part of spaces between mutually adjoining concave portions or convex portions are partially formed in a successive manner.